1. Field of the invention
This invention relates to the field of electrical instrumentation and control, and more particularly, to an instrumentation apparatus which enables the sensing of physical parameters and the control of operational functions in a remotely located A.C. powered installation.
2. The Prior Art
Numerous industrial installations exist in which an A.C. powered motor and pump assembly or other alternating current device is operated at a remote location to which access is difficult, costly and/or impractical, if not impossible. An example of such an installation is the motor and pump assembly of a submersible pumping system operating near the bottom of a subterranean bore-hole (referred to as "down-hole"). In such an installation, there is often a requirement to monitor certain physical parameters present in the down-hole environment, particularly the temperature and pressure therein. Moreover, in such installations, there will also exist the requirement to remotely control certain operational functions such as the flow of fluid through a down-hole solenoid controlled valve.
Prior art solutions to the problem of providing a communication link between a locally situated control and monitoring unit and a remotely situated control and instrumentation unit have included the use of the conductors of the 3 .phi. power supply cable for the transmission of communication signals thereby precluding the need for a separate communication pathway. Examples of such prior art systems are disclosed in U.S. Pat. Nos. 3,284,669, 3,340,500, 4,157,535, 4,178,579, 4,788,545, and 4,803,483 issued to Boyd, Boyd et al., Balkanli, McGibbeny et al., Farque, and Vandervier et al. respectively. Of these prior art systems, Farque and Vandervier et al. both transmit the communication signal over one phase of the 3 .phi. power supply, Boyd transmits the communication signal over two phases of the 3 .phi. power supply, and Boyd et al., McGibbeny et al., and Balkani all transmit the communication signal over all three phases of the 3 .phi. power supply by means of neutral points at the remote and local sites.
In those prior art systems that employ the conductors of the 3 .phi. power supply line as a conducting path, the signal transmission between the local and remote unit ranges from unidirectional and analog in the case of Boyd, Boyd et al., Farque, and Vandervier et al., to bidirectional and analog in the case of McGibbeny et al. and Balkanli.
Other prior art solutions to the problem of providing a communication link between a locally situated control and monitoring unit and a remotely situated control and instrumentation unit have simply included the use of a dedicated conductor (or conductors) for the transmission of dam. Examples of such prior art systems are disclosed in U.S. Pat. Nos. 3,406,359 and 3,991,611 issued to Welz et al. and Marshall, III et al. respectively. Of these prior art systems, Marshall, III et al. utilizes a single conductor for all communication while Welz et al. utilizes a different dedicated conductor for each piece of dam.
In those prior art systems utilizing a separate dedicated conducting path for communications, the signal transmission between the local and remote unit varies from the bidirectional serial transmission of digital information in the case of Marshall, III et al. to the unidirectional parallel transmission of analog data in the case of Welz et at.
Thus, the prior art solutions to the problem of communication between a remotely located down-hole unit and a locally located surface unit have not included: (1) the transmission of digital data by means of the conductors of the 3 .phi. power supply line; (2) the simultaneous bidirectional transmission of data (whether digital or otherwise); and/or (3) the generation and transmission of digital data by means of a modulated analog loop current.
The present invention overcomes these limitations of the prior art by permitting the simultaneous bidirectional transmission of digital dam, in the form of a modulated D.C. loop current, between a local surface unit and a remote down-hole unit by utilizing the conductors of the 3 .phi. power supply line as a signal path thereby precluding the need for a separate conducting path and at the same time permitting the rapid and reliable transmission of data between a local and a remote site.